Time proof New in 1.3

Check a time proof.

Drop an image that carries a SimpleShot time proof. You’ll see when it was stamped and whether it changed since — down to a single pixel. The check runs in this browser: the image is never uploaded.

Drop the image here, or choose a file The PNG that SimpleShot saved. If it came with a .proof.json, drop both.

What it proves.

When. The date and time on the stamp come from SimpleShot’s time server (UTC), never from the computer that made the image. The server signed the finished image’s fingerprint seconds later, with a key only it holds.
Not changed. The fingerprint covers every pixel, the stamp included. Change one pixel, crop the image or paint over the stamp, and the check says so. Renaming the file or changing its dates changes nothing.
An independent witness. Each receipt is also timestamped in the Bitcoin blockchain through OpenTimestamps, so not even SimpleShot could date one later than it was made. That takes a few hours; anyone can check it with the free ots tool.

What it doesn’t.

It proves this image existed at that moment. It doesn’t prove who made it, or that what it shows is true.
Messengers recompress photos, which changes the pixels. Send an image with a time proof as a file (a document), not as a photo.
A missing proof is not evidence of forgery: the proof can be stripped from a file, or the image never had one.

For the technically minded: the fingerprint is SHA-256 over the decoded RGBA pixels, the receipt an Ed25519 signature checked here against SimpleShot’s published key (3464a1653671275b). The key.